Lutein, together with zeaxanthin, is an essential component of the macular pigment in the retina of the eye. A low level of intake of this particular carotenoid increases the risk of age-related macular degeneration (AMD) and cataracts, which are the leading causes of visual impairment and acquired blindness, and are key quality of life issues among millions of ageing people. One of the first large-scale studies on carotenoids is the Eye Disease Case Control Study, in which diet was compared to the risk of developing AMD. Results found a significantly lower risk of developing the eye disease in people showing high amounts of lutein and zeaxanthin in their blood. Also, the people who followed a diet with the highest amounts of lutein and zeaxanthin developed a significantly lower risk of AMD than those whose diet contained the lowest amount (as low as 1.2 mg per day). Dietary studies confirmed the association between frequent consumption of spinach or collard greens, which are particular good sources of lutein and zeaxanthin and of lower AMD risk. Similar results were found in a recent analysis of a US dietary study called the Third National Health and Nutrition Examination Survey or NHANES III. This analysis also showed that consuming lutein and zeaxanthin was associated with a reduced risk of developing AMD.
Lutein (3,3′-dihydroxy-β,ε-carotene) represents an oxygenated carotenoid or xanthophyll. The conjugated double bond system determines its yellow color and is responsible for the biological activity.

The physiological properties of lutein and particularly its function as an antioxidant are due to its potential to inactivate singlet oxygen and to quench active radicals. Up to today, lutein is mainly produced synthetically since the content of this carotenoid in natural sources is considered to be rather low for any industrial production under economic conditions. In the case of fed-batch heterotrophic cultures of Chlorella protothecoides, an average lutein productivity of 22.7 m l−1 d−1 in a 3.7-L fermenter was obtained. (Biotechnol. Prog., 18, 723-727(2002)). Chlorella zofingiensis grown autotrophically in batch culture exhibited lutein contents of 20 mg/l (=4 mg/dry weight), however it grows slowly (doubling time 17.3 h) and therefore its productivity is poor (Appl. Microbiol. Biotechnol. 64, 848-654 (2004)). Muriellopsis was grown autotrophically in batch culture showing a maximal content of lutein in the cultures of 35 mg l−1 and an estimated productivity of 32.6 mg l−1 h−1 under optimized environmental and nutritional conditions of growth (J. Biotechnol. 76, 51-59 (2000)). In addition, several patents claim the use of various strains of Chlorella for the production of lutein, however, their productivity is too low for an industrial production under economic acceptable conditions (U.S. Pat. No. 4,391,291; EP 0251018 A1). Currently, lutein is produced from plants, mainly marigold flowers, which have large requirements of land showing rather low content in lutein.
The complex problem underlying the present invention has therefore been to develop a process which provides lutein from natural sources in higher yields compared to the state of the art, more particularly from algae showing simultaneously:                a specific growth rate μ at medium light conditions of at least 0.05 h−1 (measured under phototropic conditions using inorganic media);        a production of biomass per volume at medium light radiation and under phototropic conditions using inorganic media of at least 8 g dry biomass/l;        a lutein/zeaxanthin ratio of more than 5;        a factor obtained by multiplication of growth rate and lutein volumetric productivity of at least 0.02 mg l−1h−2;        a chlorophyll A /lutein ratio of less than 10, and        a volumetric lutein productivity of at least 0.2 mg l−1h−1.        
In addition, the starting material should be easy to cultivate and to harvest, so that it is possible to carry out the reaction in a photo-bioreactor. Finally, the sources should be free of any harmful toxins or be cultivated under such non-toxin-producing conditions to avoid harmful toxin formation, and be resistant against contamination.